120 DYNAMICAL GEOLOGY. 



valued when sodium chloride is mostly absent, and when carbonic acid gas 

 is present to give briskness to the waters. 



The ocean is the great mineral spring of the world ; and Artesian borings 

 over the land very often show, by bringing salt water to the surface, that 

 more or less sea water has generally been left along with the beds. About 

 S^ per cent of sea water consists of soluble salts, and of these over f is 

 common salt. When sea water along a flat shore becomes temporarily 

 confined so that it can evaporate, the salts are deposited ; first gypsum or 

 anhydrite, which goes down, according to Ursiglio, when the Beaunie areometer 

 stands at 16.75° ; and then the common salt when it is at 26.25°. While this 

 is depositing, the remaining solution, Avhich is above, holds the magnesium 

 sulphate and chloride, with the calcium chloride, and the iodide and borate, 

 and is called the " mother liquor " or " bittern " ; and it is all nearly ready 

 for deposition, the borate being among the latest although not the least solu- 

 ble. Magnesium sulphate and magnesium-potassium chloride (carnallite) 

 make much the larger part of the final depositions. But a new supply of 

 salt water at this stage may prevent deposition from the bitter magnesium 

 solution ; or the latter may be gradually drawn off to mix again with the 

 sea water, or for deposition elsewhere. Common salt dissolves in about three 

 parts of either hot or cold water ; magnesium sulphate, in about four parts 

 at 32° F., but in one third as much water at 212° F. Sodium sulphate is 

 most soluble in warm water ; hence the waters of the Great Salt Lake deposit 

 it if cooled down to 20° F. (Kussell). 



The making of salt in large shallow lagoons or " salt-pans" along seacoasts, out of 

 water let in at high tide and then confined for a time, is a common thing under the hot 

 sun of tropical countries. The same process — solar evaporation — is used in many regions 

 of brine springs. On some of the smaller coral islands of the equatorial Pacific, whose 

 lagoons had become very shallow, there are now beds of gypsum — sometimes two feet 

 thick — along with salt in places, that were made from the evaporating waters (Hague), 

 showing that the lagoon basins had passed through a salt-pan condition. 



The average composition of ocean water salts, in a hundred parts, has been deter- 

 mined by W. Dittmar to be as follows: chlorine 55-292, bromine 0-188, sulphuric acid 

 (SO3) 6-410, carbonic acid 0-152, lime 1-676, magnesia 6-209, potash 1-332, soda 41-234, 

 less the oxygen in soda and magnesia equivalent to the chlorine and bromine present 

 combined with the sodium and part of the magnesium 12-493 = 100-00 ; or combining the 

 acids and bases, the salts are : sodium chloride (common salt) 77-758, magnesium chloride 

 10-878, magnesium sulphate 4-737, calcium sulphate 3-600, potassium sulphate 2-465, 

 magnesium bromide 0-217, calcium carbonate 0-345 = 100-00. 



From these results Professor Dittmar calculates for the whole amount of salts in the 

 ocean, as follows, the unit being 1,000,000,000,000 tons: sodium chloride 35,990, mag- 

 nesium chloride 5034, magnesium sulphate 2192, calcium sulphate 1666, potassium sulphate 

 1141, magnesium bromide 100, calcium carbonate 160 — 46,283 ; also total bromine 87-2 

 (Dittmar), total iodine 0-03 (Kottstorfer), total rubidium chloride 25-0 (C. Schmidt). 



The lime alone varies appreciably with the depth. As compared with the amount of 

 chlorine and bromine (the latter calculable as chlorine) , taking the amount at 100, the lime 

 at surface (s), at medium depth (m), and in the deep sea (d) was found by Dittmar to 

 be s, 3-0175; m, 3-0300; d, 3-0308. The amount of carbonic acid m the waters above 

 what is required for calcium carbonate is large, especially that at great depths ; but it is 



